[Boost-users] Re: shared_ptrs with std::mem_fn

From: David Abrahams (dave_at_[hidden])
Date: 2004-05-07 20:13:01

"Mark Storer" <MStorer_at_[hidden]> writes:

> So why won't std::mem_fun work through boost::shared_ptr's
> operator->?
>
> Here's the mem_fun that ships with VC6:
>
> ---
> template<class _R, class _Ty>
> 	class mem_fun_t : public unary_function<_Ty *, _R> {
> public:
> 	explicit mem_fun_t(_R (_Ty::*_Pm)())
> 		: _Ptr(_Pm) {}
> 	_R operator()(_Ty *_P) const
                  ^^^^^^^
> 		{return ((_P->*_Ptr)()); }
> private:
> 	_R (_Ty::*_Ptr)();
> 	};
> ---
>
> The relevant portion to our discussion is: 
>     "{return ((_P->*_Ptr()); }" 
> which can be further boiled down to:
>     return _P->_Ptr();

No, the relevant part is the signature I highlighted above.

> This looks an awful lot like it should work with a shared_ptr's
> operator->().  So why doesn't it?

It should be obvious now, I hope.

> I admit that this is more of a C++ question than a boost one, but
> it's not too much of a tangent and I *am* curious.

All I have to say is "use boost::mem_fn, which works, and never
touch the one in std::".

-- 
Dave Abrahams
Boost Consulting
http://www.boost-consulting.com